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At least 829 records · Page 46Linked to original sources
USGS1995

Surface-geophysical techniques used to detect existing and infilled scour holes near bridge piers

Surface-geophysical techniques were used with a position-recording system to study riverbed scour near bridge piers. From May 1989 to May 1993, Fathometers, fixed- and swept-frequency continuous seismic- reflection profiling (CSP) systems, and a ground-penetrating radar (GPR) system were used with a laser-positioning system to measure the depth and extent of existing and infilled scour holes near bridge piers. Equipment was purchased commercially and modified when necessary to interface the components and (or) to improve their performance. Three 200-kHz black-and-white chart-recording Fathometers produced profiles of the riverbed that included existing scour holes and exposed pier footings. The Fathometers were used in conjunction with other geophysical techniques to help interpret the geophysical data. A 20-kHz color Fathometer delineated scour-hole geometry and, in some cases, the thickness of fill material in the hole. The signal provided subbottom information as deep as 10 ft in fine-grained materials and resolved layers of fill material as thin as 1 ft thick. Fixed-frequency and swept-frequency CSP systems were evaluated. The fixed-frequency system used a 3.5-, 7.0-, or 14-kHz signal. The 3.5-kHz signal penetrated up to 50 ft of fine-grained material and resolved layers as thin as 2.5-ft thick. The 14-kHz signal penetrated up to 20 ft of fine-grained material and resolved layers as thin as 1-ft thick. The swept-frequency systems used a signal that swept from 2- to 16-kHz. With this system, up to 50 ft of penetration was achieved, and fill material as thin as 1 ft was resolved. Scour-hole geometry, exposed pier footings, and fill thickness in scour holes were detected with both CSP systems. The GPR system used an 80-, 100-, or 300-megahertz signal. The technique produced records in water up to 15 ft deep that had a specific conductance less than 200 µS/cm. The 100-MHz signal penetrated up to 40 ft of resistive granular material and resolved layers as thin as 2-ft thick. Scour-hole geometry, the thickness of fill material in scour holes, and riverbed deposition were detected using this technique. Processing techniques were applied after data collection to assist with the interpretation of the data. Data were transferred from the color Fathometer, CSP, and GPR systems to a personal computer, and a commercially available software package designed to process GPR data was used to process the GPR and CSP data. Digital filtering, predictive- deconvolution, and migration algorithms were applied to some of the data. The processed data were displayed and printed as color amplitude or wiggle-trace plots. These processing methods eased and improved the interpretation of some of the data, but some interference from side echoes from bridge piers and multiple reflections remained in the data. The surface-geophysical techniques were applied at six bridge sites in Connecticut. Each site had different water depths, specific conductance, and riverbed materials. Existing and infilled scour holes, exposed pier footings, and riverbed deposition were detected by the surveys. The interpretations of the geophysical data were confirmed by comparing the data with lithologic and (or) probing data.

Connecticut↗
USGS1999

Ten years of studies on Maryland's inner Continental Margin and coastal bays

During the past ten years of the Association of American State Geologists-Mineral Management Service Continental Margins Program, the Maryland Geological Survey investigated the sedimentological, paleontological, stratigraphical and geophysical character of Maryland's inner continental shelf. Based on seismic records and sedimentological analyses completed during the first four years, a late Quaternary stratigraphic model was developed. Five distinct stratigraphic units were identified and described on the Maryland inner shelf. These units represent late Pleistocene interglacial deposits, the oldest of which corresponds to pre-Illinoian (oxygen-isotope stages 7 and/or 9) transgressive shelf sands. Overlying the Q1 unit, the Q2 unit is a 6-meter thick mud sequence of oxygen-isotope stage 5 (128-75 ka) age. Units Q3 and Q4 representing fluvial and leading edge estuarine deposits (oxygen-isotope stages 4, 3 and 2) filled numerous paleochannels that were incised into units Q2 and Q1. Modern trailing-edge transgressive shelf shoals (Unit Q5) discontinuously cap the sequence. The 5th and 6th years studies reported on the economic minerals of surficial and cored sediments. Vibracores collected off the Maryland's shelf during previous studies were analyzed for mineral types and abundances, weight percent of general size fractions, and heavy mineral (HM) content. Mineralogic maturity indices were compiled to correlate the THM and economic heavy minerals (EHM) abundances with position offshore, sediment type, and the indices themselves. For the 7th year, the Maryland Geological Survey re-examined geophysical records and lithological data originally collected by the Army Corps of Engineers to locate and assess beach fill borrow areas for the Ocean City Beach Replenishment Project. Data from 163 vibracores and over 300 kilometers of high-resolution seismic profile records collected off Ocean City, Maryland, supported the stratigraphic model developed by MGS during the first four years of the AASG-MMS program. The Maryland coastal bays became the focus of study during the 8th and 9th years during which seismic records, cores and surficial sediment were collected in Isle of Wight and Assawoman Bays. Shallow pretransgression surface was mapped, relating the existing streams to offshore paleochannels. The tenth year study focused on developing a repository for vibracores collected on Maryland's inner continental shelf.During the past ten years of the Association of American State Geologists-Mineral Management Service Continental Margins Program, the Maryland Geological Survey investigated the sedimentological, paleontological, stratigraphical and geophysical character of Maryland's inner continental shelf. Based on seismic records and sedimentological analysis completed during the first four years, a late quaternary stratigraphic model was developed. Five distinct stratigraphic units were identified and described on the Maryland inner shelf. These units represent late Pleistocene interglacial deposits, the oldest of which corresponds to pre-Illinoian transgressive shelf sands.

Marine Georesources and Geotechnology↗
USGS2019

Lithologic descriptions, geophysical logs, and source-rock geochemistry of the U.S. Geological Survey Alcova Reservoir AR–1–13 Core Hole, Natrona County, Wyoming

In 2013, a continuous 624-foot core hole was drilled and logged by the U.S. Geological Survey in Natrona County, Wyoming, with the goal to better understand Cretaceous source rocks in the Wind River Basin. The core hole, named the Alcova Reservoir AR–1–13, penetrated the interval extending from the upper part of the Lower Cretaceous Cloverly Formation to the lower part of the Upper Cretaceous Frontier Formation. The lithologies are predominantly mudrock, with minor amounts of sandstone and altered volcanic ash beds that were deposited in open marine, nearshore marine, and fluvial settings. Samples were collected from open marine clay-rich, dark-colored mudrocks, and these were analyzed for total organic carbon content and by programmed pyrolysis analysis. The results show that the lower part of the Frontier Formation, Shell Creek Shale equivalent, and the Thermopolis Shale contain Type III gas-prone kerogen, with poor to fair generative source rock potential. The upper part of the Mowry Shale has good to excellent generative potential, with organic matter composed mainly of Type II oil-prone kerogen with some mixed Type II/III kerogen capable of generating oil and gas.

Wyoming↗
USGS2014

The use of resistivity‐methods in the location of salt‐water bodies in the El Paso, Texas, Area

During 1935 and 1936 the Ground‐Water Division of the United States Geological Survey made an investigation of the ground‐water resources of the El Paso, Texas, Area. Geological and hydrological studies comprised the principal part of the investigation, and these studies were supplemented by measurements of earth‐resistivity made largely by the Geophysical Section of the Geological Survey along traverses aggregating 51 miles. The extent to which resistivity‐methods may be useful in ground‐water work has been the subject of much discussion. A full evaluation of the method can not be made at this time. However, the work in the El Paso Area indicates that the presence of faults and of underground bodies of salt water may be definitely determined by resistivity‐measurements.

Texas↗
USGS1977

Mineral resources of the Sheep Mountain Wilderness study area and the Cucamonga Wilderness and additions, Los Angeles and San Bernardino counties, California

A mineral survey of the Sheep Mountain Wilderness study area and Cucamonga Wilderness area and additions by the U.S. Geological Survey and Bureau of Mines in 1975 covered about 66,500 acres (26,500 ha) of the San Bernardino and Angeles National Forests in southern California. The two study areas are separated by San Antonio Canyon. The mineral resource potential was evaluated through geological, geochemical, and geophysical studies by the Geological Survey and through evaluation of mines and prospects by the Bureau of Mines.

California↗
USGS1993

The Hatu gold anomaly, Xinjiang-Uygur Autonomous Region, China - testing the hypothesis of aeolian transport of gold

In 1987, a cooperative project between the U.S. Geological Survey and the Institute of Geophysical and Geochemical Exploration was initiated to evaluate the origin of the Hatu gold anomaly. The anomaly is located in the Hatu mining district in the northwest corner of Xinjiang-Uygur Autonomous Region in northwest China. The climate is semiarid to arid and wind erosion predominates. A regional soil survey of the Hatu district, based on samples collected on a 200 by 500 m grid and composited prior to chemical analysis to a density of one sample per square km, delineated a series of south-southeast-trending Au anomalies. Anomalous Au values range from 5 ppb to more than 700 ppb. The Hatu anomaly, the most prominent of these anomalies, is more than 30 km long and about 5 km wide. The mining town of Hatu and the economic gold deposits of Qiqu 1 and Qiqu 2 are at the northern end of this anomaly. The axis of the Hatu anomaly cuts across mapped structure and stratigraphy in the district, but is parallel to the prevailing wind direction. This observation led to the hypothesis that the Hatu anomaly is the result of acolian dispersion of gold from the vicinity of Qiqu 1 and Qiqu 2. The alternative interpretation, that the anomalies reflected additional primary gold occurrences, was not consistent with existing information on the known occurrences and the geology.

Journal of Geochemical Exploration↗
USGS2012

Scientific basis for safely shutting in the Macondo Well after the April 20, 2010 Deepwater Horizon blowout

As part of the government response to the Deepwater Horizon blowout, a Well Integrity Team evaluated the geologic hazards of shutting in the Macondo Well at the seafloor and determined the conditions under which it could safely be undertaken. Of particular concern was the possibility that, under the anticipated high shut-in pressures, oil could leak out of the well casing below the seafloor. Such a leak could lead to new geologic pathways for hydrocarbon release to the Gulf of Mexico. Evaluating this hazard required analyses of 2D and 3D seismic surveys, seafloor bathymetry, sediment properties, geophysical well logs, and drilling data to assess the geological, hydrological, and geomechanical conditions around the Macondo Well. After the well was successfully capped and shut in on July 15, 2010, a variety of monitoring activities were used to assess subsurface well integrity. These activities included acquisition of wellhead pressure data, marine multichannel seismic profiles, seafloor and water-column sonar surveys, and wellhead visual/acoustic monitoring. These data showed that the Macondo Well was not leaking after shut in, and therefore, it could remain safely shut until reservoir pressures were suppressed (killed) with heavy drilling mud and the well was sealed with cement.

Gulf of Mexico↗
USGS2024

Recent expansion of the Cascades Volcano Observatory geophysical network at Mount Rainier for improved volcano and lahar monitoring

The U.S. Geological Survey Cascades Volcano Observatory (CVO) recently expanded its continuous geophysical monitoring at Mount Rainier, an active stratovolcano in Washington state. CVO monitors volcanoes in Oregon, Washington, and Idaho to characterize volcanic systems and detect unrest. Mount Rainier has a history of large lahar occurrences in the Holocene, including at least one that may not have been associated with volcanic activity. Pierce County, Washington, is one of the areas most at risk from large lahars. In the 1990s, CVO collaborated with Pierce County to install the Rainier lahar detection system (RLDS), an automated system designed to detect large lahars in high‐risk drainages and mitigate hazards to heavily populated areas. The system was designed to detect lahars within 5–10 min of their occurrence and alert authorities of the need to evacuate populated low‐lying areas before lahar arrival. In addition, CVO and the Pacific Northwest Seismic Network (PNSN) maintained and expanded a network of seismic and geodetic monitoring stations on and near the edifice to provide adequate volcano monitoring capabilities. Since 2016, CVO has worked to upgrade the existing RLDS and to expand its capabilities into other drainages around Mount Rainier. This expansion includes installation of 25 new broadband seismic stations with many including infrasound along high‐risk drainages, as well as support for equipment upgrades at existing PNSN and CVO volcano monitoring sites. All stations transmit continuous, near‐real‐time data with dramatically improved spatial coverage for volcano monitoring and lahar hazard mitigation compared to the previous system.

Washington↗
USGS1949

Calculated gravity anomaly produced by possible fault under line 27-48

The seismograph data from Line 27-48 of Party 47 indicates the possibility of a high angle fault win a displacement of roughly 1,000 feet under South Barrow Test Well No. 2. This fault vas discussed in E. Wiancko's report for United Geophysical Company entitled "Report of Reflection Seismograph Survey in the Barrow Area During 1948". Mr. Delta. and Mr. English recently expressed a desire to know the magnitude of the calculated gravity anomaly produced by this probable fault. Their purpose was to determine the feasibility of proving and locating this fault, if exists, by several traverses with the gravimeter. As interpreted in Wiancko's report, the fault is nearly east-west in strike and is a reverse fault with the up-thrust block on the north side. The assumptions made for the calculation of the theoretical anomaly were that the density of the basement rock was 2.7, the density of the overlying rocks was 2.2 and the fault itself was taken directly from Plate I, Drawing No. 2044, of Wiancko's report, simplified, and reduced by a factor of 2. The calculated anomaly is shown in Fig. 1. A polar chart similar to the type described on pages 153-154 of Heiland's "Geophysical Exploration" was used in computing the value of the anomaly. It was assumed that the feature is two-dimensional. Broken lines indicate values of limited accuracy. It should be mentioned here that Mr. Roland Henderson and Mr. Isidore Zietz of the Section of Geophysics of the Geological Survey carried out the calculations and plotted Fig. 1.

Alaska↗
USGS1997

Hydrogeologic evaluation of the Upper Floridan aquifer in the southwestern Albany area, Georgia

A cooperative study by the Albany Water, Gas, and Light Commission and the U.S. Geological Survey was conducted to evaluate the hydrogeology of the Upper Floridan aquifer in an area southwest of Albany and west of the Flint River in Dougherty County, Ga. The study area lies in the Dougherty Plain district of the Coastal Plain physiographic province. In this area, the Upper Floridan aquifer is comprised of the upper Eocene Ocala Limestone, confined below by the middle Eocene Lisbon Formation, and semiconfined above by the undifferentiated Quaternary overburden. The overburden ranges in thickness from about 30 to 50 feet and consists of fine to coarse quartz sand, clayey sand, sandy clay, and clay. The Upper Floridan aquifer has been subdivided into an upper water-bearing zone and a lower water-bearing zone based on differences in lithology and yield. In the study area, the upper water-bearing zone generally consists of dense, highly weathered limestone of low permeability and ranges in thickness from 40 to 80 feet. The lower water-bearing zone consists of hard, slightly weathered limestone that exhibits a high degree of secondary permeability that has developed along fractures and joints, and ranges in thickness from about 60 to 80 feet. Borehole geophysical logs and borehole video surveys indicate two areas of high permeability in the lower water-bearing zone-one near the top and one near the base of the zone. A wellfield consisting of one production well and five observation-well clusters (one deep, intermediate, and shallow well in each cluster) was constructed for this study. Spinner flowmeter tests were conducted in the production well between the depths of 110 and 140 feet below land surface to determine the relative percentages of water contributed by selected vertical intervals of the lower water-bearing zone. Pumping rates during these tests were 1,080, 2,200, and 3,400 gallons per minute. The results of these pumping tests show that the interval between 118 and 124 feet below land surface contributes a significant percentage of the total yield to the well. An aquifer test was conducted by pumping the production well at a constant rate of 3,300 gallons per minute for about 49 hours. Time-dependent water-level data were collected throughout the pumping and recovery phases of the test in the pumped well and the observation wells. The maximum measured drawdown in the observation wells was about 2.6 ft. At about 0.5 mile from the pumped well, there was little measurable effect from pumping. Water levels increased during the test in wells located within about 3.75 miles of the Flint River (about 0.5 miles east of the pumping well). This water-level increase correlated with a 3.5-feet increase in the stage of the Flint River. The hydraulic characteristics of the Upper Floridan aquifer were evaluated using the Hantush-Jacob curve-matching and Jacob straight-line methods. Using the Hantush-Jacob method, values for transmissivity ranged from about 120,000 to 506,000 feet squared per day; values for storage coefficient ranged from 1.4 x 10-4 to 6.3 x 10-4; and values for vertical hydraulic conductivity of the overlying sediments ranged from 4.9 to 6.8 feet per day. Geometric averages for these values of transmissivity, storage coefficient, and vertical hydraulic conductivity were calculated to be 248,000 feet squared per day, 2.7 x 10-4, and 5.5 feet per day, respectively. If a dual porosity aquifer model (fracture flow plus matrix flow) is assumed instead of leakage, and the Jacob straight-line method is used with late time-drawdown data, the calculated transmissivity of the fractures ranged from about 233,000 to 466,000 feet squared per day; and storage coefficient of the fractures plus the matrix ranged from 5.1 x 10-4 to 2.9 x 10-2.

Georgia↗
USGS2011

Geophysical data collected from the St. Clair River between Michigan and Ontario, Canada (2008-016-FA)

In 2008, the U.S. Geological Survey (USGS), Woods Hole Coastal and Marine Science Center (WHCMSC), in cooperation with the U.S. Army Corps of Engineers conducted a geophysical and sampling survey of the riverbed of the Upper St. Clair River between Port Huron, Mich., and Sarnia, Ontario, Canada. The objectives were to define the Quaternary geologic framework of the riverbed of the St. Clair River to evaluate the relationship between morphologic change of the riverbed and underlying stratigraphy. This report presents the geophysical and sample data collected from the St. Clair River, May 29-June 6, 2008, as part of the International Upper Great Lakes Study, a 5-year project funded by the International Joint Commission of the United States and Canada to examine whether physical changes in the St. Clair River are affecting water levels within upper Great Lakes, to assess regulation plans for outflows from Lake Superior, and to examine the potential effect of climate change on the Great Lakes water levels (http://www.iugls.org). This document makes available the data that were used in a separate report, U.S. Geological Survey Open-File Report 2009-1137, which detailed the interpretations of the Quaternary geologic framework of the region. This report includes a description of the high-resolution acoustic and sediment-sampling systems that were used to map the morphology, surficial sediment distribution, and underlying geology of the Upper St. Clair River during USGS field activity 2008-016-FA (http://quashnet.er.usgs.gov/cgi-bin/datasource/public_ds_info.pl?fa=2008-016-FA). Video and photographs of the riverbed were also collected and are included in this data release. Future analyses will be focused on substrate erosion and its effects on river-channel morphology and geometry. Ultimately, the International Upper Great Lakes Study will attempt to determine where physical changes in the St. Clair River affect water flow and, subsequently, water levels in the Upper Great Lakes.

Open-File Report↗
USGS2002

Interpretation of borehole geophysical logs, aquifer-isolation tests, and water quality, supply wells 1 and 2, Willow Grove Naval Air Station/Joint Reserve Base, Horsham Township, Montgomery County, Pennsylvania

Ground water pumped from supply wells 1 and 2 on the Willow Grove Naval Air Station/Joint Reserve Base (NAS/JRB) provides water for use at the base, including potable water for drinking. The supply wells have been contaminated by volatile organic compounds (VOC's), particularly trichloroethylene (TCE) and tetrachloroethylene (PCE), and the water is treated to remove the VOC's. The Willow Grove NAS/JRB and surrounding area are underlain by sedimentary rocks of the Triassic-age Stockton Formation, which form a complex, heterogeneous aquifer. The ground-water-flow system for the supply wells was characterized by use of borehole geophysical logs and heatpulse-flowmeter measurements. The heatpulse-flowmeter measurements showed upward and downward borehole flow under nonpumping conditions in both wells. The hydraulic and chemical properties of discrete water-bearing fractures in the supply wells were characterized by isolating each water-bearing fracture with straddle packers. Eight fractures in supply well 1 and five fractures in supply well 2 were selected for testing on the basis of the borehole geophysical logs and borehole television surveys. Water samples were collected from each isolated fracture and analyzed for VOC?s and inorganic constituents. Fractures at 50–59, 79–80, 196, 124–152, 182, 241, 256, and 350–354 ft btoc (feet below top of casing) were isolated in supply well 1. Specific capacities ranged from 0.26 to 5.7 (gal/min)/ft (gallons per minute per foot) of drawdown. The highest specific capacity was for the fracture isolated at 179.8–188 ft btoc. Specific capacity and depth of fracture were not related in either supply well. The highest concentrations of PCE were in water samples collected from fractures isolated at 236.8–245 and 249.8–258 ft btoc, which are hydraulically connected. The concentration of PCE generally increased with depth to a maximum of 39 mg/L (micrograms per liter) at a depth of 249.8? 258 ft btoc and then decreased to 21 mg/L at a depth of 345.3–389 ft btoc. Fractures at 68–74, 115, 162, 182, 205, and 314 ft btoc were isolated in supply well 2. Specific capacities ranged from 0.08 to less than 2.9 (gal/ min)/ft. The highest specific capacity was for the fracture isolated at 157–165.2 ft btoc. Concentrations of detected VOC's in water samples were 3.6 mg/L or less. Lithologic units penetrated by both supply wells were determined by correlating naturalgamma and single-point-resistance borehole geophysical logs. All lithologic units are not continuous water-bearing units because water-bearing fractures are not necessarily present in the same lithologic units in each well. Although the wells penetrate the same lithologic units, the lithologic location of only three water-bearing fractures are common to both wells. The same lithologic unit may have different hydraulic properties in each well. A regional ground-water divide is southeast of the supply wells. From this divide, ground water flows northwest toward Park Creek, a tributary to Little Neshaminy Creek. Potentiometric-surface maps were prepared from water levels measured in shallow and deep wells. For both depth intervals, the direction of ground-water flow is toward the northwest. For most well clusters, the vertical head gradient is downward from the shallow to the deeper part of the aquifer. Pumping of the supply wells at times can cause the vertical flow direction to reverse.

Water-Resources Investigations Report↗
USGS2014

Geophysical logging of bedrock wells for geothermal gradient characterization in New Hampshire, 2013

The U.S. Geological Survey, in cooperation with the New Hampshire Geological Survey, measured the fluid temperature of groundwater and other geophysical properties in 10 bedrock wells in the State of New Hampshire in order to characterize geothermal gradients in bedrock. The wells selected for the study were deep (five ranging from 375 to 900 feet and five deeper than 900 feet) and 6 had low water yields, which correspond to low groundwater flow from fractures. This combination of depth and low water yield reduced the potential for flow-induced temperature changes that would mask the natural geothermal gradient in the bedrock. All the wells included in this study are privately owned, and permission to use the wells was obtained from landowners before geophysical logs were acquired for this study. National Institute of Standards and Technology thermistor readings were used to adjust the factory calibrated geophysical log data. A geometric correction to the gradient measurements was also necessary due to borehole deviation from vertical. Maximum groundwater temperatures at the bottom of the logs ranged from 11.2 to 15.4 degrees Celsius. Geothermal gradients were generally higher than those typically reported for other water wells in the United States. Some of the high gradients were associated with high natural gamma emissions. Groundwater flow was discernible in 4 of the 10 wells studied but only obscured the part of the geothermal gradient signal where groundwater actually flowed into, out of, or through the well. Temperature gradients varied by mapped bedrock type but can also vary by localized differences in mineralogy or rock type within the wells.

New Hampshire↗
USGSDate not supplied

Integrated geophysical characterization of the Winthrop Landfill Southern Flow Path, Winthrop, Maine

The U.S. Geological Survey (USGS), in cooperation with United Technologies Corporation, used an integrated suite of borehole, surface, and water-borne geophysical methods near the site of the former Winthrop Landfill, Winthrop, Maine, to investigate the hydrogeology controlling the transport of leachate from the landfill to nearby Annabessacook Lake. During the fall of 2000 and summer of 2001, the USGS conducted borehole electromagnetic (EM) induction and gamma logging, and inductive terrain-conductivity, two-dimensional (2D) resistivity, continuous seismic reflection, and magnetic surveys. The objectives of this integrated geophysical study were to provide constraints on the location and extent of the southern flow path(s) of contamination from the landfill to the lake; identify shoreline seep geophysical signatures; identify potentially hidden seeps in the lake; and determine depth to bedrock below Annabessacook Lake in the study area. Interpretation of surface 2D resistivity, magnetic, and inductive terrain-conductivity data and borehole EM logs delineates an electrically conductive anomaly consistent with a leachate plume moving from the current landfill boundary southward through the overburden to the shores of Annabessacook Lake. Surface and borehole geophysical data collected south and southeast of the landfill indicate the presence of discrete, shallow conductive anomalies at the southeastern edge of the landfill and near the lakeshore. The conductive anomalies appear at increasing depths closer to the lake. Magnetic anomalies offshore confirm the presence of iron-rich landfill leachate discharging into the lake south of the landfill. High-resolution swept-frequency seismic data used to map sediment and grain size distribution in the lake sub-bottom along the shoreline identified sediment-infilled bedrock lows that may act as conduits for contaminant migration.

Maine↗
USGS2012

The problem of groundwater discharge into the seas

Introductory Note: The dynamic equilibrium of the various factors involved in the world water balance or budget is the central scientific problem of the International Hydrological Decade. One of the potentially vital elements of the balance is groundwater discharge to the oceans. To paraphrase the authors of the following Russian publication, the world water budget can't be properly balanced, statically or dynamically, until there are improved values for the amount of groundwater that is discharged directly to oceans, seas, and enclosed lakes. The following report, with its bibliography, presents some Russian approaches to the problem and provides a few bits of numerical information. The report was translated by Frank W. Trainer of the U.S. Geological Survey. The text has been slightly reduced in the interests of saving space but the bibliography is given in full and has been transcribed into more or less standard U.S. Geological Survey bibliographical style. ©1971. American Geophysical Union. All Rights Reserved.

Eos, Transactions, American Geophysical Union↗
USGS2000

Mount St. Helens - From the 1980 eruption to 2000

Mount St. Helens, Washington, is the most active volcano in the Cascade Range. Its most recent series of eruptions began in 1980 when a large landslide and powerful explosive eruption created a large crater, and ended 6 years later after more than a dozen extrusions of lava built a dome in the crater. Larger, longer lasting eruptions have occurred in the volcano's past and are likely to occur in the future. Although the volcano seems to have returned to a period of quiet, scientists with the U.S. Geological Survey and University of Washington Geophysics Program continue to closely monitor Mount St. Helens for signs of renewed activity.

Washington↗
USGS2000

Borehole-radar methods: Tools for characterization of fractured rock

Locating and characterizing bedrock fractures and lithologic changes is an important component of studies of ground water supply and contamination in fractured-rock aquifers. Borehole-radar reflection methods provide information on the location, orientation, and lateral extent of fracture zones that intersect the borehole, and can identify fractures in the rock surrounding the borehole that are not penetrated by drilling. Crosshole radar logging provides crosssectional maps of the electromagnetic properties of bedrock between boreholes that can identify fracture zones and lithologic changes and can also be used to monitor tracer tests. Borehole-radar logs can be integrated with results of surfacegeophysical surveys and other borehole-geophysical logs, such as acoustic or optical televiewer and flowmeter, to distinguish transmissive fractures from lithologic variations or closed fractures. Integrated interpretation procedures provide results that can be used to develop conceptual and numerical models, design monitoring and sampling programs, and monitor implementation of contamination remediation measures, such as blast-fracturing.

Fact Sheet↗